This invention relates generally to the fields of molecular biology and molecular medicine and more specifically to proteins involved in the regulation of immunological response and cell death.
Programmed cell death is a physiologic process that ensures homeostasis is maintained between cell production and cell turnover in essentially all self-renewing tissues. In many cases, characteristic morphological changes, termed “apoptosis,” occur in a dying cell. Since similar changes occur in different types of dying cells, cell death appears to proceed through a common pathway in different cell types.
In addition to maintaining tissue homeostasis, apoptosis also occurs in response to a variety of external stimuli, including growth factor deprivation, alterations in calcium levels, free-radicals, cytotoxic lymphokines, infection by some viruses and bacteria, radiation and most chemotherapeutic agents. Thus, apoptosis is an inducible event that likely is subject to similar mechanisms of regulation as occur, for example, in a metabolic pathway. In this regard, dysregulation of apoptosis also can occur and is observed, for example, in some types of cancer cells, which survive for a longer time than corresponding normal cells, and in neurodegenerative diseases where neurons die prematurely. In viral and certain bacterial infections, induction of apoptosis can figure prominently in the pathophysiology of the disease process, because immune-based eradication of viral or bacterial infections depend on elimination of virus or bacteria-producing host cells by immune cell attack resulting in apoptosis.
It has long been recognized that viruses harbor genes that regulate apoptosis of host cells, making vital contributions to the virus life-cycle. Some types of bacteria, such as Chlamiydiae species, have also been found to regulate apoptosis in host cells. Previous studies have established that infection of mammalian cells with Chlamydiae species can either suppress or induce apoptosis, depending on whether examined early or late in the infection cycle of these obligate intracellular bacteria. However, the bacterial genes responsible for the regulation of host cell apoptosis are not known.
Tumor Necrosis Factor (TNF) family cytokines play an important role in a wide variety of immunological, allergic, and inflammatory responses. Several members of the TNF family have been identified, including TNFα, Lymphotoxin-α, Lymphotoxin-β, LIGHT, CD27 Ligand (CD27L), CD30L, CD40L, Fas-L, Trail, and others. These molecules are generally produced as Type-II integral membrane proteins on the surface of cells, undergoing subsequent release into the excellular milieu as a result of proteolytic cleavage. Many of the TNF-family cytokines however remain anchored in the plasma membrane, relying on interactions with receptor-bearing cells through cell-cell contact. The receptors for TNF-family cytokines are equally diverse. All members of the family have a conserved arrangement of cysteines in their extracellular domains, which is one of the criteria for membership in this family.
The intracellular cytosolic domain of TNF-family receptors are diverse in their amino acid sequences, but can be broadly classified into two types: (a) those that contain a protein-interaction module known as a Death-Domain (TNFR1, Fas, DR3, DR4, DR5, DR6, p75NTR) and those that do not (TNFR2, CD27, CD30, CD40, LTβR, 4B1 and others). Death Domains are responsible for interactions of a subgroup of the TNF-Receptor (TNFR) family with adapter proteins which bind in turn to caspase-family intracellular proteases involved in inducing apoptosis (programmed cell death). However, the Death Domains can also mediate binding to other types of adaptor molecules which bind kinases or other types of signaling molecules rather than proteases. For example, several death domain proteins participate in regulation of NFκB induction during an inflammatory response.
Although some of the proteins involved in programmed cell death have been identified and associations among some of these proteins have been described, additional apoptosis regulating proteins remain to be found. Furthermore, the mechanisms by which these proteins mediate their activity remains to be elucidated. The identification of the proteins involved in cell death and an understanding of the associations between these proteins can provide a means for manipulating the process of apoptosis in a cell and, therefore, selectively regulating the relative lifespan of a cell or its relative resistance to cell death stimuli.
The identification of new proteins or new domains within known proteins, and the elucidation of the proteins with which they interact, can form the basis for strategies designed to alter apoptosis, cytokine production, cytokine receptor signaling, and other cellular processes. Such new proteins can thus be used to develop therapeutic applications for controlling apoptosis.
Thus, a need exists to identify novel apoptosis-related domains within both novel and known proteins. The present invention satisfies this need and provides additional advantages as well.